2015 Kenworth W900 — Battery Size & Group (CCA, Specs, Replacement)

Quick answer

• BCI group size: Group 31 (commercial)
• System voltage: 12V
• Quantity: Typically three Group 31 batteries in parallel from the factory; some builds use four for cold climates or high hotel loads/APU use
• Cold cranking amps (CCA): 700–950 CCA per battery (recommend 900+ CCA each for cold-weather service). Combined CCA equals the sum of each battery in parallel
• Reserve capacity (RC): About 180–220 minutes at 25A per battery (AGM tends to be on the higher end)
• Battery type: Flooded lead-acid is acceptable; AGM is recommended for vibration resistance and deep-cycle hotel loads, but not strictly required
• Terminal layout: Top threaded studs (3/8-16) commonly used on Class 8 trucks; some batteries also offer dual stud/SAE posts—match what your cables use
• Physical dimensions (Group 31): ~13.0 in L x 6.8–6.9 in W x 9.3–9.5 in H (330 x 173 x 240 mm). Verify your battery box and hold-down style
• Dual/tri/quad setup: Parallel 12V pack (3 or 4 batteries). Do not mix ages or chemistries; replace the full set together

Replacement battery options

These are well-supported Group 31 commercial batteries commonly used in Class 8 trucks. Always match group size, terminal type (stud), and height for your Kenworth battery box and hold-downs.

• Interstate: Group 31 commercial (available in flooded and AGM). Widely used in fleets; choose stud terminals and 900+ CCA for cold climates
• Odyssey: Extreme Series Group 31 AGM (high CCA and excellent cycle life for sleeper/idle-shutdown duty)
• DieHard: Commercial Group 31 (flooded or AGM offerings; select stud terminal variant with appropriate CCA/RC)
• ACDelco: Professional/Gold Group 31 (available in flooded and AGM; pick stud terminal version and heavy-duty vibration rating)
• Optima: Group 31 options are limited; verify terminal type and automotive/HD rating. Some marine-oriented 31 models may not provide the preferred 3/8-16 studs—confirm compatibility before purchase

Note: Part numbers vary by chemistry, terminal style, and height; consult the brand’s HD/commercial catalog for the exact Group 31 stud-terminal variant for the W900. Never mix different battery models or ages within the same pack.

AGM vs flooded — which does this vehicle need?

The 2015 Kenworth W900 does not require AGM by specification; flooded Group 31 batteries are acceptable and common. However, AGM offers tangible benefits in this application:

• Superior vibration resistance in frame-rail battery boxes
• Better performance under deep cycling from sleeper loads, APUs, inverters, and frequent idle-shutdown
• Faster recharge acceptance from high-output alternators

Choose AGM if the truck runs heavy hotel loads, short-trip routes, or harsh vibration environments. Flooded batteries are cost-effective for long-haul operations with minimal hotel loads and good maintenance practices. Whichever you choose, install the same chemistry and model across the entire pack.

Post-installation relearn / reset procedure

Most W900s do not require special ECM relearn after battery replacement, but a clean power-up sequence helps avoid nuisance faults:

1. Park safely, set parking brakes, and switch the cab/master battery disconnect to OFF.
2. Replace all batteries as a matched set. Clean and inspect cables, grounds, and hold-downs. Use anti-corrosion protectant.
3. Connect batteries in parallel correctly: positives tied together, negatives tied together, then connect truck positive leads first, negative leads last. Verify all lugs are tight and supported. Match stud hardware to 3/8-16 if applicable.
4. Turn the master disconnect ON. Key ON (engine off) for ~30 seconds to let modules initialize.
5. Start and let the engine idle 5–10 minutes with major accessories off so the alternator can stabilize charge rate.
6. Verify charging voltage (typically ~13.8–14.4V at the battery bank once warmed) and check for warning lamps. Clear any transient ABS/ATC lights with a short road test; they usually self-clear after key cycles and movement.
7. Re-enter radio clock/presets and any aftermarket ELD/telematics settings if they reset during the power loss.

Tip: If the truck has memory-sensitive devices, a temporary power supply can be used during service, but most vocational/line-haul W900s tolerate a full power-down without special programming.

Signs of a failing battery

• Slow or uneven crank, especially after an overnight park
• Clicking from the starter solenoid or intermittent no-crank
• Dim headlights or cabin lights at idle with accessories on
• Electronics dropping out when using sleeper loads or liftgate/inverter
• Excessive sulfation/corrosion on terminals, wet tops, or case swelling
• Repeated jump-starts or low open-circuit voltage after sitting

Common battery issues for this generation

• Vibration damage in frame-rail battery boxes leading to plate shedding—ensure tight, intact hold-downs
• Corroded grounds and starter feed cables causing voltage drop; inspect frame grounds and starter connections regularly
• Parasitic draws from telematics, ELDs, APUs, refrigerators, and inverters accelerating discharge when parked
• Mixing old and new batteries or flooded with AGM in the same pack—causes imbalance and shortens life
• Water intrusion and road spray in the battery box leading to green corrosion and premature failure; maintain box seals and drains
• Alternator undercharge/overcharge from long cable runs or failed voltage sense wiring; verify charge voltage at the battery bank, not just at the alternator
• Improper terminal hardware (wrong stud size or loose hardware) causing heat and intermittent no-starts

Find a trusted shop on Repairius.